Three-dimensionally braided hollow fiber module for mass and energy transfer operations

ABSTRACT

The invention relates to a hollow fiber bundle for accommodation in a mass transfer device, the hollow fiber bundle including a multitude of hollow fiber strands for heat transfer and/or mass transfer which are aligned essentially at least locally along a preferential direction and are arranged with respect to one another in relation to their local preferential directions such that at least one first group of hollow fiber strands points essentially in a first preferential direction, at least one second group of hollow fiber strands essentially in a second preferential direction and at least one third group of hollow fiber strands in essentially a third preferential direction, the three preferential directions being independent of one another.

RELATED APPLICATION

The present application is a National Phase entry of PCT Application No. PCT/EP2010/061988, filed Aug. 27, 2010, which claims priority from German Application Number 102009038673.4, filed Aug. 24, 2009, the disclosures of which are hereby incorporated by reference herein in their entirety.

TECHNICAL FIELD

The invention relates to a hollow fiber bundle for accommodation in a mass transfer device, and to a mass transfer device for accommodating at least one such hollow fiber bundle as well as a method for manufacturing a hollow fiber bundle for accommodation in a mass transfer device.

BACKGROUND

The field of use of mass transfer devices ranges from general industrial applications in chemistry or physics to applications in medical technology. Mass transfer devices relate to the transfer of a mass, which may be present in a gaseous or even liquid phase, between a first phase and a second phase separated from the latter by a permeable membrane. The mass transfer ensues in this case due to a concentration or pressure gradient between the first and second phases. Depending on the mass or masses exchanged, respectively the phase in which these masses are present, the membrane's configuration requires fundamental technical conditions so as to be able to guarantee a desired mass transfer.

Although not merely limited to medical engineering applications, a medical engineering application shall be mainly assumed in the following, on the basis of which essential principles will be explained.

In medical engineering applications for mass transfer, the elimination of harmful substances, respectively the transfer of health-promoting or life-sustaining substances from or into the patent's body, are usually of major focus. A concern of hemodialysis, for instance, is to purify a patient's blood of harmful degradation products or toxic substances. In the case of oxygenators, supplying sufficient oxygen to a patient's blood is in the foreground on the one hand while, on the other, the blood also needs to be purified of the carbon dioxide produced. Further typical mass transfer devices of medical technology may, for example, be realized for plasma separation (blood separation) or for hybrid organs such as the artificial liver.

If a mass transfer between a patient's blood and a further transfer phase such as a gas mixture with oxygen is to take place, it must be ensured that the patient's blood is sufficiently treated; i.e. the mass transfer proceeds sufficiently. As a consequence, care has to be taken with oxygenators that enough oxygen from the transfer phase is introduced into the patient's blood via the membrane. It likewise has to be taken into account that a sufficient amount of the carbon dioxide which accumulates is removed from the patient's blood. Depending on the mass transfer volume, oxygenators can be used, for example, merely for supporting the natural pulmonary function, respectively for the complete substitution thereof. In this case, it is for example possible to provide oxygenators externally as well as internally within a patient's blood circulation in order to replace the patient's pulmonary function during a surgical operation.

Depending on the requirements, the necessary membranes exhibit specific material properties and geometries so as to allow the desired mass transfer. Many modern mass transfer devices in medical technology use membranes of hollow fibers, the fiber walls of which have a predefined permeability for a substance to be transferred. Such membranes can be made of suitable polymeric plastics as well as polymeric polypropylene or polymeric polymethyl pentene or else of silicone. According to the prior art, a plurality of hollow fibers of parallel orientation are in this case typically combined into a mat in order to obtain a larger overall transfer surface. Such mats may be used in a single layer or also in a multi-layer respectively. With a layer made from a plurality of mats, the axes of longitudinal extension to the hollow fibers of different mats adhere to defined divergence angles to one another so as to prevent single hollow fibers from nesting within one another. In an oxygenator, these layers of mats are then essentially arranged in the form of a hollow cylinder so as to subject blood that flows in the radial direction of this cylinder to a mass transfer when passing through individual hollow fibers. As representative of this widespread technique in medical technology, reference is made to patent document EP 0 621 047 B1, in which the designated hollow fibers are present in double-layer, cross-wound hollow fiber mats each having a plurality of hollow fibers arranged in parallel. The hollow fibers of one hollow fiber mat are in this case stitched together with parallel warps perpendicular to the axis of longitudinal extension of the individual hollow fibers of one hollow fiber mat so as to restrict the movement of the individual hollow fibers relative to one anther. The alignment of the hollow fibers of the first hollow fiber mat relative those of the second hollow fiber mat are, for instance, at an angle of 22°. Furthermore, the individual hollow fiber mats are layered over one another as applicable and rolled up into a bundle, with the ends of the hollow fibers being embedded in a tube by means of a resin to thereby anchor them.

Apart from geometric limitations, mass transfer devices typically have to meet a range of performance requirements resulting from safety aspects related to patient care as well as medical considerations. For example, the blood filling volume has to hereby be considered as does a drop in pressure on the transfer phase side (e.g. a gas with oxygen in an oxygenator) as well as the blood side phase, the shearing stress of blood cells and the properties of the membrane surfaces and surface effects upon interaction with blood. Solutions are continually being proposed in medical technology which take the multitude of influences into account but in which improvements in fulfilling certain requirements are achieved at the expense of degenerating the fulfillment of other requirements. An important parameter for the efficiency and hence the amount of the substance transferred in a mass transfer device are the local temperatures and also the local temperature differences between the blood phase and the transfer phase. Thus, modern oxygenators, for example, also comprise integrated heat exchangers which are intended to largely equalize temperature differences within the mass transfer device during mass transfer, e.g. by using heat-conducting materials in a plate-shaped construction.

To be able to improve the mass transfer in mass transfer devices, in particular the oxygen transfer in oxygenators, the following Equation 1 can be viewed as mathematically describing the gas transfer rate in the oxygenator.

dV/dt=K·A·Δp _(ln)   (1)

Here, dV/dt designates the gas transfer rate between the gaseous transfer phase within the hollow fibers and the blood phase outside the hollow fibers. The gas transfer rate dV/dt is hereby calculated as the product of an overall mass transfer coefficient (K), the size of the membrane surface (A), and the logarithmic mean value of the partial gas pressure (Δp_(ln)) which represents the driving potential of the mass transfer. The mass transfer coefficient K may be described as a function of individual mass transfer coefficients for the respective gas in the gas phase, membrane and blood phase (not described in greater detail herein).

It will become obvious from the above equation that numerous measures can be taken theoretically for improving the mass transfer in a mass transfer device. Technical practice, however, shows that many measures to improve one parameter are accompanied by the deterioration of another parameter. In particular when hollow fibers are used in mass transfer devices, technical efforts have mainly been focused on optimizing the shape of the mass transfer device's housing, the positioning of the individual hollow fibers and influencing the blood phase flow within the mass transfer device. Despite these efforts, however, many serious disadvantages are seen in many mass transfer devices known from prior art which cause a reduced mass transfer. These comprise, for example, wall effects of the blood phase between the inner housing wall and the external hollow fibers, channel formations, short-circuit flows and dead zones, all of which entail a significantly reduced mass transfer between the transfer phase in the hollow fibers and the blood phase.

Particularly with the arrangement of a plurality of hollow fibers in a hollow fiber mat, respectively a plurality of such mats in a hollow fiber bundle, the phenomena described above can then be specifically confirmed when the hollow fiber mats, respectively hollow fiber bundles, are wound around a cylinder arranged centrally within the mass transfer device. In this case, not only are there short-circuit flows of radially flowing blood which can flow from the interior of the cylinder directly to the inner walls thereof virtually without entering an interacting mass transfer having a hollow fiber. Moreover, significant wall effects between the hollow fiber mat and the inner wall of the cylinder can sometimes also occur in such configurations, whereby the desired mass transfer is greatly reduced.

SUMMARY

According to the disadvantages presented above, it may thus be recognized as being necessary to propose an arrangement of hollow fibers, a hollow fiber bundle respectively, which is provided for accommodation in a mass transfer device and which reduces the disadvantages described above which give rise to a reduced mass transfer in the mass transfer device. In particular, embodiments relate to a hollow fiber bundle which allows for an improved mass transfer when accommodated in a mass transfer device. Embodiments also relate to a corresponding mass transfer device for accommodating at least one hollow fiber bundle, as well as a method for manufacturing such a hollow fiber bundle.

According to embodiments, this task is addressed by embodiments of a a hollow fiber bundle for accommodation in a mass transfer device. The task is moreover addressed by a method for manufacturing a hollow fiber bundle for accommodation in a mass transfer device.

The task is in particular addressed in embodiments by a hollow fiber bundle for accommodation in a mass transfer device wherein the hollow fiber bundle comprises a plurality of hollow fiber strands for mass transfer and/or heat transfer which are aligned at least locally essentially along a preferential direction, are arranged with respect to one another in terms of their local preferential directions such that at least one first group of hollow fiber strands points essentially in a first preferential direction, at least one second group of hollow fiber strands points essentially in a second preferential direction, and at least one third group of hollow fiber strands in essentially a third preferential direction, wherein said three preferential directions are independent of one another.

Furthermore, the task is addressed in embodiments by a hollow fiber bundle for accommodation in a mass transfer device, wherein the hollow fiber bundle comprises at least one hollow fiber strand for mass transfer or mass and heat transfer which comprises a plurality of hollow fibers interbraided with one another.

The task is moreover addressed in embodiments by a mass transfer device for accommodating at least one hollow fiber bundle, wherein at least one hollow fiber bundle is realized in accordance with a hollow fiber bundle.

The task is in addition addressed in embodiments by a method for manufacturing a hollow fiber bundle for accommodation in a mass transfer device, the method comprising: providing at least one plurality of hollow fibers for mass or mass and heat transfer; and arranging at least one plurality of said hollow fibers in at least one hollow fiber strand by interbraiding.

Embodiments provide a plurality of hollow fiber strands in a hollow fiber bundle, wherein different hollow fiber strands have different preferential directions in space so that a three-dimensional structure is formed. Hollow fiber strands in the meaning according to the invention can be both single hollow fibers as well as a plurality of hollow fibers. In case of single hollow fibers, the preferential direction of the hollow fiber strands is defined by the longitudinal extension of the hollow fibers, and in case of a hollow fiber strand having a plurality of hollow fibers, by the strand's essentially mean longitudinal direction of extension. Accordingly, the hollow fibers are always interconnected so that a preferential direction can be defined.

Since individual hollow fibers as well as hollow fiber strands in the hollow fiber bundle can in addition exhibit bends, the hollow fiber bundle is characterized by a three-dimensional structure which at least locally comprises hollow fibers, respectively hollow fiber strands, that exhibit three mutually independent spatial directions. The independence of individual preferential directions is to be understood mainly in the mathematical meaning so that a three-dimensional structure is formed from three hollow fibers, respectively hollow fiber strands, having independent preferential directions. Here and in the following, one independent preferential direction will be equated to one different preferential direction.

The three-dimensional arrangement of hollow fiber strands in the hollow fiber bundle consequently allows achieving the most optimum utilization of space possible on the one hand and, on the other, obtaining a geometric hollow fiber scaffolding which conditions the dynamic flow of the phase passing by the outer surface of the hollow fiber walls. Thus, in oxygenators, for example, it is of decisive importance for the blood phase to achieve an appropriate turbulent flow at least in areas, whereby the contact with the surfaces of the hollow fiber walls is statistically improved, on the one hand, and also an appropriate thorough mixing of the blood phase takes place, on the other. In particular in hollow fiber mats known from the prior art which in most cases locally define only a two-dimensional structure, respectively a structure having only two preferential directions, the degree of turbulence developing in the blood phase is often only very low.

Additionally, embodiments further obtain a hollow fiber strand by interbraiding several hollow fibers, whereby an auto-stabilizing structure is realized on the one hand, and, on the other, said structure exhibits a surface topography which due to the single hollow fibers interlacing with one another (interbraiding) in turn locally achieves an improvement of the turbulent flow of the phase moving past at the surface of the hollow fiber strand. Furthermore, individual hollow fiber strands made from a plurality of hollow fibers show to be extraordinarily suited to obtain larger hollow fiber bundles by being connected respectively bundled in a modular construction.

In the preceding as well as in the following, interbraiding of single hollow fibers together is to be understood in the meaning of single hollow fibers being interlaced with one another. The interlacing in this case, however, is performed such that the braided hollow fibers create a stable structure so as to prevent individual hollow fibers from disengaging from said structure by themselves. Moreover, it should be pointed out that an interbraiding of individual hollow fibers comprises at least two hollow fibers which are not guided at a right angle to one another. Thus, interbraiding differs fundamentally from interweaving or intercrossing, in which the hollow fibers are essentially in two groups of hollow fibers entwined in an intercrossed manner. Consequently, it is also comprehensible that, due to the relatively low limitation with respect to the arrangement of single hollow fibers strands, respectively hollow fibers, to one another, interbraiding allows for a by far more important spectrum of possible realizations of hollow fiber bundles.

In one embodiment, the hollow fiber bundle is characterized in that at least one of the hollow fiber strands is composed of a plurality of hollow fibers. Since the mechanical stability of a hollow fiber strand made from a plurality of hollow fibers is improved as compared to single hollow fibers, this will also result in an improvement of the mechanical stability of the entire hollow fiber bundle as a whole. This improvement then in particular arises when the plurality of hollow fibers is fixed to one another so as to prevent single hollow fibers from shifting with respect to one another. Such an anchoring can be achieved for example by an appropriate interlinking by means of retaining elements or retaining fibers, or else by simply gluing to one another. In place of retaining elements or retaining fibers, the anchoring can also be achieved by further transversely running hollow fibers.

One further developed embodiment provides for the plurality of hollow fibers of the at least one hollow fiber strand to be interbraided. Due to the interbraiding, the surfaces of the hollow fibers are aligned with respect to each other, respectively the hollow fibers are so entwined, that a slipping, respectively shifting, of individual hollow fibers in a hollow fiber strand is not possible or only to a reduced extent. This accordingly results in a more mechanically stable structure as compared to a single hollow fiber. Furthermore, the entire surface of a hollow fiber strand can be conditioned by appropriately interbraiding individual hollow fibers so as to advantageously influence the flow of the phase coming into contact with the surface of the hollow fibers.

In one further embodiment, a hollow fiber bundle comprises at least one hollow fiber strand for mass transfer or mass and heat transfer, which itself further preferably comprises a plurality of hollow fibers interbraided with one another. In the case of mass and heat transfer, at least one hollow fiber is provided for mass transfer and at least one hollow fiber for heat transfer.

In one further embodiment of the hollow fiber bundle the interbraiding of the hollow fibers is realized such that same mutually stabilize each other. Consequently, a more stable structure to the hollow fiber bundle results even when at least three groups of hollow fiber strands are interbraided in at least locally different preferential directions. The interbraiding hence allows the hollow fiber bundle to be formed as a whole using appropriate braiding techniques. The mechanical stabilizing of the hollow fiber bundle mainly turns out to be necessary when the phase coming into contact with the outer surface of the hollow fiber in the use of the mass transfer device exerts a flow pressure on same. According to the embodiment, the stabilization resulting from the interbraiding of the hollow fibers is sufficient to be able to resist such a flow pressure without essentially changing the structure of the hollow fiber bundle.

In one further embodiment, the at least one hollow fiber strand of the hollow fiber bundle is interconnected within the hollow fiber bundle having at least one further hollow fiber strand for mass transfer or mass and heat transfer comprising a plurality of hollow fibers interbraided together. The hollow fiber bundle can consequently be formed from a number of hollow fiber strands which in turn are formed from a plurality of hollow fibers. The interconnecting of individual hollow strands can be realized by appropriate means such as connecting fibers or loops or also connecting elements. Connecting by means of gluing or else by interbraiding is moreover possible.

In one further embodiment of the hollow fiber bundle, the hollow fiber bundle comprises two groups of hollow fiber strands which point in two mutually independent preferential directions. Each hollow fiber strand may in this case further comprise a plurality of single hollow fibers interbraided together. Consequently, arranging individual hollow fiber bundles having different preferential directions in turn enables a particularly advantageous, relatively flexible constitution of three-dimensional structures of a hollow fiber bundle.

In one further embodiment, the hollow fiber bundle comprises exactly three groups of hollow fiber strands, each pointing in one preferential direction which is independent of the other preferential directions. This in turn allows the particularly preferred forming of an appropriate hollow fiber bundle according to given dimensions such as of the housing of a mass transfer device.

In one further developed embodiment, the exactly three preferential directions are essentially arranged perpendicular to one another. The perpendicular arrangement with respect to one another allows the forming of particularly stable structures of the hollow fiber bundle, since the flow forces arising within the hollow fiber bundles can be largely distributed equally over all of the three spatial directions. Precisely in the case of hollow fiber bundles in which a turbulent flow is set in one of the phases at least in areas, an appropriate force transmission can consequently take place in all spatial directions.

Furthermore, one embodiment provides for the first group of hollow fiber strands, the second group of hollow fiber strands, and the third group of hollow fiber strands to be interbraided. A connection by means of interbraiding is, on the one hand, relatively simple to realize and, on the other, results in a stable hollow fiber bundle structure.

In one further development, the interbraiding of the first group of hollow fiber strands, the second group of hollow fiber strands, and the third group of hollow fiber strands is realized such that a self-supporting structure able to withstand mechanical loads is created as a result. The load-bearing capacity of this structure is at least sufficient to resist the flow pressure arising within the hollow fiber bundle.

According to one further embodiment, the interbraiding forms a regular structure with respect to the hollow fiber strands. A regular structure is particularly crucial for a uniform thorough mixing of the phase coming into contact with the outer surface of the hollow fiber. Different mass transfer efficiencies, respectively interference or dead flows or also dead volumes, can accordingly be largely avoided or even completely prevented in areas. Preferably, the regular structure has a symmetry which can even correspond to the symmetry of the shape of the mass transfer device's housing, as need be.

According to one further embodiment of the hollow fiber bundle, the first group of hollow fiber strands and the second group of hollow fiber strands are provided for mass transfer, and the third group of hollow fiber strands is provided for heat exchange. As a consequence, temperature gradients within the fiber bundle can be relatively well equalized even locally. In particular for mass transfer devices which need to guarantee a heat level of high constancy within the hollow fiber bundle—e.g. in oxygenators—heat can be introduced, respectively discharged, essentially in the entire volume of the hollow fiber bundle. Accordingly, it can be guaranteed for the phase coming into contact with the outer surfaces of the hollow fibers to have a largely constant temperature across the volume of the hollow fiber bundle. By varying this temperature via a corresponding discharging, respectively transferring, of heat, the mass transfer rate within the hollow fiber bundle can also be appropriately adjusted.

One embodiment of the hollow fiber bundle further provides for the first group of hollow fiber strands and the second group of hollow fiber strands to form one channel or a plurality of channels essentially along the preferential direction of the third group of hollow fiber strands. By means of the channels, an appropriate flow conditioning of the phase which comes into contact with the outer surfaces of the hollow fibers can be achieved. As a consequence, the entire mass transfer rate can again be influenced in a targeted manner.

In another embodiment of the hollow fiber bundle, the hollow fibers of at least one hollow fiber strand are at least in areas positioned by the holes of one or more perforated discs. With same, the hollow fibers can be easily connected to a fluid supply system in particular at the terminal end, wherein same is mechanically fixed in the area of the perforated discs. The perforated discs are in this case adapted to receive single hollow fibers respectively hollow fiber bundles of several hollow fibers.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described below on the basis of exemplary embodiments which are explained in greater detail by means of the figures. Shown are:

FIG. 1 is a schematic sectional view through one embodiment of a hollow fiber bundle.

FIG. 2 is a schematic sectional view through one further embodiment of a hollow fiber bundle.

FIG. 3 is a schematic representation of arranging hollow fiber strands in a hexagonal form according to a further embodiment.

FIG. 4 is a mathematical depiction of the longitudinal distribution s₁ and the porosity ε of a hollow fiber bundle as per the embodiment indicated in FIG. 3;

FIG. 5 is an exemplary representation of an embodiment of a hollow fiber strand having three hollow fibers;

FIG. 6 is an exemplary representation of a further embodiment of a hollow fiber strand.

FIG. 7 is an exemplary representation of a further embodiment of a hollow fiber strand.

FIG. 8 is a lateral sectional view through one embodiment of a mass transfer device for accommodating a hollow fiber bundle.

DETAILED DESCRIPTION

The same reference numerals will be used in the following description for identical parts or parts with identical effect.

FIG. 1 shows a schematic sectional view through a first embodiment of a hollow fiber bundle 1 which comprises a total of three groups of different hollow fiber strands 10 a, 10 b and 10 c, their respective preferential directions V1, V2 and V3 being independent of one another. The preferential directions in particular are arranged such that the first group of hollow fiber strands 10 a has the preferential direction V1, the second group of hollow fiber strands 10 b the preferential direction V2, and the third group of hollow fiber strands 10 c the preferential direction V3. For a clearer representation, only two hollow fiber strands 10 a, each of which are formed by two hollow fibers 11, as well as two hollow fiber strands 10 b, each of which are likewise formed by two hollow fibers 11, are illustrated. The two hollow fiber strands 10 a are thereby each arranged in one plane, and the two hollow fiber strands 10 b in a plane situated directly above. The planes in the present case are not further designated by reference numerals but can be easily identified on the basis of the graphical representations. Preferential direction V1 of the first group of hollow fiber strands 10 a, and preferential direction V2 of the second group of hollow fiber strands 10 b are in this case situated perpendicular above one another. The two hollow fibers 11 of each hollow fiber strand 10 a respectively 10 b are interbraided with the hollow fiber strands 10 c of the third group of hollow fiber strands 10 c by interlacing. For better recognition, the first and second group of hollow fiber strands 10 a and 10 b appear to be thinner in the illustration than the hollow fibers 11 of the third group of hollow fiber strands 10 c. However, all of the hollow fibers 11 of the three groups of hollow fiber strands 10 a, 10 b and 10 c can hereby be of identical outer diameter.

In the sectional view, the third group of hollow fiber strands 10 c comprises in each case three hollow fibers 11 at the edge side of the hollow fiber bundle 1 which are arranged in a triangular configuration to one another in the cross-section illustrated in FIG. 1. Further hollow fiber strands 10 c arranged according to the sectional view in FIG. 1 inside the hollow fiber bundle 1 only comprise one hollow fiber 11 and are arranged according to the illustrated sectional view in extension to one of the edge-side hollow fiber strands 10 c such that they are aligned on the paper plane in a linear arrangement to one another. Thus, the designated interior hollow fiber strands 10 c are arranged such that three hollow fiber strands 10 c consisting in each case of one hollow fiber 11, are in each case arranged between two hollow fiber strands 10 c, each of which comprises three hollow fibers 11. It is thus possible to interbraid hollow fibers 11 in a plane arranged perpendicular to the preferential direction V3 by interlacing with the single hollow fiber strands 10 c essentially arranged parallel to one another. For interlacing one hollow fiber 11 of e.g. the first group of hollow fiber strands 10 a, one hollow fiber is thereby guided between two hollow fibers 11 of the laterally arranged hollow fiber strands 10 c in the hollow fiber bundle 1, in order to subsequently wind around the above-designated hollow fiber strands 10 c of the hollow fiber bundle 1 which are situated further inside, and consequently be interbraided with same.

The present illustration reflects a schematic view of a first possible embodiment of the hollow fiber bundle 1, however with only two planes of hollow fiber strands 10 a and 10 b being depicted. For a better understanding, the illustration as per FIG. 1 additionally exhibits numerous auxiliary lines which allow the relative arrangement of the single hollow fiber strands 10 c to one another to be better identified. According to the embodiment, however, only the three mutually different groups of hollow fiber strands 10 a, 10 b and 10 c form a physical part of the hollow fiber bundle. The person skilled in the art will comprehend that any arbitrary number of planes of hollow fiber strands 10 a and 10 b can be arranged in an alternating manner along the preferential direction V3 by interlacing with the individual hollow fiber strands 10 c. Consequently, a cubic hollow fiber bundle 1 can, for example, be formed, respectively a square one, the extension of which along the preferential direction V3 is defined by the longitudinal extension of the hollow fiber strands 10 c. The interbraiding of the hollow fiber strands 10 a with the hollow fiber strands 10 c, respectively the hollow fiber strands 10 b with the hollow fiber strands 10 c, as well as the alternating sequence of these arrangements along preferential direction V3 create a mechanically stable hollow fiber bundle 1.

In an embodiment, the hollow fiber strands 10 c are also provided for heat transfer in the hollow fiber bundle 1, whereas the two hollow fiber strands of the group of hollow fiber strands 10 a and 10 b are provided for mass transfer. In case of using the hollow fiber bundle 1 in an oxygenator, the first and second groups of hollow fiber strands 10 a and 10 b would consequently be perfused by oxygen so as to exchange same in the blood phase (not shown in the present figure). Furthermore, a CO₂ exchange would also occur between the blood phase and the gas phase flowing in the hollow fibers 11. In contrast thereto, the hollow fiber strands 10 c of the third group could be perfused by a heat exchange fluid which guarantees a largely uniform heat distribution within the hollow fiber bundle 1. According to the embodiment, the hollow fibers 11 of the hollow fiber strands 10 c can be realized to be comparable to, respectively different from, the two groups of hollow fiber strands 10 a and 10 b. In particular, it should be noted that the individual hollow fibers 11 can have a typical inner diameter of 200 μm to 280 μm and a typical outer diameter of 300 μm to 380 μm.

For the individual groups of hollow fiber strands 10 a, 10 b and 10 c to be filled with the respective fluid, same can be subjected to an appropriate fluid pressure via connecting pieces into which they are glued or sealed, for instance. Accordingly, a defined flow of a fluid can also be set in the individual groups of hollow fiber strands 10 a, 10 b and 10 c in a targeted manner.

In comparison to FIG. 1, FIG. 2 shows a further possible embodiment of a hollow fiber bundle 1 in a cross-sectional view. In this case, the individual hollow fiber strands 10 c, each consisting of one hollow fiber 11, of the third group of hollow fiber strands form a braiding point for the hollow fibers 11 interlaced with same of the first group of hollow fiber strands 10 a and the second group of hollow fiber strands 10 b in a cross-section along the preferential direction V3. The braiding point essentially defines the crossing point illustrated in the present cross-sectional view of two hollow fibers 11 forming a hollow fiber strand 10 a or 10 b. In comparison hereto, the hollow fiber strands 10 c of the embodiment shown in FIG. 1 which are each formed by one hollow fiber 11 do not need to exhibit braiding points. Instead, only two of the three hollow fibers 11 of one group of hollow fiber strands 10 c constitute a braiding point. Depending on the manner of braiding, a denser, respectively stronger, braided structure of the hollow fiber bundle 1 can be formed. Different manners of braiding in particular allow for setting a different porosity for the hollow fiber bundle 11 resulting from the relationship of free volume in the hollow fiber bundle 1 to the total volume of the hollow fiber bundle 1.

FIG. 3 shows a schematic cross-sectional view of an abstracted hollow fiber bundle 1 (not shown in the present figure) which is provided for accommodation in a hexagonal housing of a mass transfer device 2 (not shown in the present figure). In this case, the cross-sectional view illustrated in FIG. 3 is comparable to the cross-sectional view illustrated in FIGS. 1 and 2. The first and second groups of hollow fiber strands 10 a and 10 b are not, however, depicted in FIG. 3. The third group of hollow fiber strands 10 c is only shown schematically by one hollow fiber strand 10 c comprising three hollow fibers 11. The housing shape which is realized to be hexagonal in the present case is reflected by a peripheral line to the housing 3.

According to the embodiment, the arrangement of the three hollow fibers 11 of the illustrated hollow fiber strand 10 c can be optimized with regard to the angle of inclination β so as to constitute an interbraiding of individual hollow fibers 11 having a desired geometry and porosity to the hollow fiber bundle 1. The angle β is in this case defined by the angle between the idealized lateral boundary line of the illustrated square reference pattern and the connecting line through the respective center points of the two hollow fibers 11 of the hollow fiber strand 10 c situated closest to said boundary line. Accordingly, a hollow fiber bundle 1 having a predefined porosity can be created as a function of the arrangement of the three hollow fibers 11 to one another; i.e. also as a function of the illustrated angle β. The porosity can also be realized as a function of the transverse distribution s_(q) and the longitudinal distribution s₁ of the hollow fibers 11. The longitudinal distribution s₁ is here defined in the meaning of the spacing between two hollow fibers in the axial direction (along the longitudinal extension of the hollow fibers 11). The transverse distribution s_(q) results from the spacing between two hollow fibers 11 in the radial direction (perpendicular to the longitudinal extension of the hollow fibers 11). Calculating an appropriate angle β on the one hand allows the wall effects to be determined when the hollow fiber bundle is used in a mass transfer device 2, as well as the magnitude of flow circulating around the hollow fibers comprised by the hollow fiber bundle 1. In this case, it is in turn comprehensible that the hollow fibers can be provided in groups for different tasks (mass transfer, heat transfer).

One exemplary calculation of the longitudinal distribution s₁ and the porosity ε as a function of the angle β for the configuration illustrated in FIG. 3 can be noted from FIG. 4. Here, the parameters of the transverse distribution s_(q) were set at 150 μm and the outer diameter d_(a) of one hollow fiber 11 at 380 μm. The illustrated calculations make clear that with an increasing angle β, both the longitudinal distribution s₁ as well as the porosity ε of the hollow fiber bundle 1 will increase. According to the two illustrated curves, it is now possible to set an appropriate longitudinal distribution s₁ as well as an appropriate porosity ε for a predetermined mass transfer device 2. It should hereby be pointed out again that the porosity ε results from the relationship of the free volume of the hollow fiber bundle 1 to the total volume of the hollow fiber bundle 1.

An appropriate arrangement, in particular an oblique arrangement of the hollow fibers 11 within the mass transfer device 2, can guarantee that the condensation water which typically can form in a gas phase flowing through the mass transfer device 2 will drip off. Accordingly, there will be no blockages or undesired forming of pools.

An appropriate interbraiding of individual hollow fibers 11, respectively individual hollow fiber strands 10 a, 10 b or 10 c, within one hollow fiber bundle 1 allows for setting not only different packing geometries but also different porosities. This property shows to be of particular significance when hollow fiber bundles 1 are formed for accommodation in artificial organs (hybrid organs) such as in an artificial liver, for example.

FIG. 5 shows one possible embodiment of a hollow fiber strand 10 a which has three individual hollow fibers 11. The appropriate interbraiding of the three hollow fibers 11 allows the forming of a hollow fiber strand 10 a which has an improved mechanical stability compared to the individual hollow fibers 11. In addition, the depicted hollow fiber strand 10 a has a characteristic surface topography which can appropriately condition the flow of a phase contacting the surface of the individual hollow fibers 11 with respect to its flow dynamics. Thus, particularly in oxygenators, the formation of local turbulences is desired in order to increase the statistical contact probability of individual blood components with the surfaces of the individual hollow fibers 11.

In comparison to FIG. 5, FIG. 6 shows an alternative interbraiding of individual hollow fibers 11, wherein however two different groups of perpendicular hollow fiber strands 10 a and 10 c are provided one above the other in FIG. 6. The interbraiding of the individual hollow fibers 11 of the hollow fiber strand 10 a can in this case take place in clearly defined planes but also in such a manner that the individual hollow fibers 11 will not run in clearly definable planes. Such an embodiment is illustrated in FIG. 7, for example, where only the hollow fibers 11 extending perpendicular to the paper plane lie in a clearly definable plane but not the hollow fibers 11 of the hollow fiber strand 10 a interlaced with same.

Depending on the requirement, an appropriate bundling into a hollow fiber bundle 1 can be achieved by the appropriate interbraiding of individual hollow fibers 11, respectively hollow fiber strands 10 a, 10 b and 10 c. The hollow fiber strands 10 a respectively 10 c illustrated in FIGS. 5 to 7 are hereby to be typically understood as subunits of a larger hollow fiber bundle 1 constituted by arranging a plurality of similar structures. Moreover, it will be clear to the person skilled in the art that any further forms of interbraiding can be applied, in particular when using various arbitrary numbers of hollow fibers.

FIG. 8 shows a lateral cross-sectional view of one embodiment of a mass transfer device 2 in which one embodiment of the inventive hollow fiber bundle 1 is accommodated. Here, the hollow fiber bundle 1 is only shown schematically. In particular, the hollow fiber bundle 1 exhibits only one first group of hollow fiber strands 10 a and one third group of hollow fiber strands 10 c in the illustration. A second group of hollow fiber strands 10 b can be arranged in the preferential direction V2 perpendicular to the paper plane.

The hollow fibers 11 of the hollow fiber bundle 1 are connected to the necessary inlets respectively outlets of the mass transfer device 2 via appropriate connecting pieces. The mass transfer device 2 in particular comprises an inlet 41 for a transfer medium, a blood inlet 41 in the case of an oxygenator, via which the transfer medium flows into the mass transfer device 2 perpendicular to the preferential direction V1 of the first group of hollow fiber strands 10 a and perpendicular to the preferential direction V2 of the second group of hollow fiber strands 10 b. After having flown through the mass transfer device 2, the transfer medium is discharged via an outlet 42, a blood outlet 42 in the case of an oxygenator. For supplying the first group of hollow fiber strands 10 a with an appropriate transfer phase, a gas inlet 43, an O₂ inlet 43 in the case of an oxygenator, is provided through which oxygen can flow into the hollow fiber strands 10 a and is discharged again from the mass transfer device 2 through a gas outlet 44, a O₂/CO₂ outlet 44 in the case of an oxygenator, after having completed the mass transfer and passing through the mass transfer device 2 along the preferential direction V1. Further inlets respectively outlets can be provided. In particular, an arbitrary number of inlets and outlets can be provided to supply the second groups of hollow fiber strands 10 b arranged in the preferential direction V2.

The present mass transfer device 2 in addition exhibits a third group of hollow fiber strands 10 c which are provided for heat transfer respectively heat regulation. The hollow fiber strands 10 c are hereby equipped with appropriate connections via which a heat medium can be introduced respectively discharged. The present embodiment correspondingly exhibits an inlet 45 for a heat medium as well as an outlet 46 for a heat medium.

It is to be emphasized at this point that all of the components described above, in particular the details illustrated in the drawings, whether taken alone or in any combination, are claimed as being essential to the invention. The person skilled in the art will be familiar with modifications thereof. 

1. A hollow fiber bundle for accommodation in a mass transfer device, the hollow fiber bundle comprising: a plurality of hollow fiber strands for at least one of mass transfer or heat transfer which are aligned at least locally essentially along a preferential direction, are arranged with respect to one another in terms of their local preferential directions such that at least one first group of hollow fiber strands points essentially in a first preferential direction, at least one second group of hollow fiber strands points essentially in a second preferential direction, and at least one third group of hollow fiber strands essentially in a third preferential direction, wherein said three preferential directions are independent of one another.
 2. The hollow fiber bundle according to claim 1, wherein at least one of the hollow fiber strands comprises a plurality of hollow fibers.
 3. The hollow fiber bundle according to claim 2, wherein the plurality of hollow fibers of the at least one hollow fiber strand are interbraided together.
 4. A hollow fiber bundle for accommodation in a mass transfer device, wherein one hollow fiber bundle comprises at least one hollow fiber strand for at least one of mass transfer or mass and heat transfer and which in turn comprises a plurality of hollow fibers interbraided together.
 5. The hollow fiber bundle according to claim 4, wherein the interbraiding of the hollow fibers is realized such that same mutually stabilize each other.
 6. The hollow fiber bundle according to claim 4, characterized in that wherein the at least one hollow fiber strand, in relation to at least one further hollow fiber strand, for at least one of mass transfer or mass and heat transfer is interconnected within the hollow fiber bundle to a plurality of hollow fibers interbraided together.
 7. The hollow fiber bundle according to claim 4, wherein the hollow fiber bundle comprises two groups of hollow fiber strands which point in two mutually independent preferential directions.
 8. The hollow fiber bundle according to claim 4, wherein the hollow fiber bundle comprises exactly three groups of hollow fiber strands which each point in one preferential direction which is independent from the other preferential directions.
 9. The hollow fiber bundle according to claim 8, wherein the exactly three preferential directions are arranged essentially perpendicular to one another.
 10. The hollow fiber bundle according to claim 8, wherein the first group of hollow fiber strands, the second group of hollow fiber strands, and the third group of hollow fiber strands are interbraided with one another.
 11. The hollow fiber bundle according to claim 10, wherein the interbraiding of the first group of hollow fiber strands, the second group of hollow fiber strands, and the third group of hollow fiber strands is realized such that a self-supporting structure able to withstand mechanical loads is created as a result.
 12. The hollow fiber bundle according to claim 3, wherein the interbraiding forms a regular structure with respect to the hollow fiber strands.
 13. The hollow fiber bundle according to claim 1, wherein the first group of hollow fiber strands and the second group of hollow fiber strands are provided for mass transfer, and the third group of hollow fiber strands is provided for heat transfer.
 14. The hollow fiber bundle according to claim 1, wherein the first group of hollow fiber strands and the second group of hollow fiber strands form at least one of one channel or a plurality of channels essentially along the preferential direction of the third group of hollow fiber strands.
 15. The hollow fiber bundle according to claim 2, wherein the hollow fibers of at least one hollow fiber strand are positioned at least in areas by the hole of one or more perforated discs.
 16. A mass transfer device for accommodating at least one hollow fiber bundle, comprising at least one hollow fiber bundle is formed according to claim
 1. 17. A method for manufacturing a hollow fiber bundle for accommodation in a mass transfer device comprising: providing at least one plurality of hollow fibers for at least one of mass or mass and heat transfer; and arranging at least one plurality of the hollow fibers in at least one hollow fiber strand by interbraiding. 